OCEANSIDE, N.Y. (CBSNewYork) — Thousands of patients at a Long Island hospital have been put on alert, warning that they could have been infected with hepatitis and HIV.

As CBS 2’s Tracee Carrasco reported Tuesday night, South Nassau Communities Hospital in Oceanside said patients being treated for diabetes may have received insulin injections from a pen reservoir that might have been used with more than one patient.

More than 4,000 patients have received, or may soon receive, a disturbing letter in the mail about the risk.

The component that might have been reused was the reservoir – the part of the insulin pen where the hormone is held until injection — and not the single-use needle, the statement said.

The pens each contain multiple insulin doses with disposable needles. While nurses used new needles for each patient, they did not use a fresh pen.

Blood may have back-flowed into the chamber contaminating the insulin, the hospital warned.

In a statement, a hospital spokesman said while “the risk of infection from this is extremely low, nonetheless, out of an abundance of caution, the hospital is recommending that patients receiving the notification be tested for hepatitis B, hepatitis C and HIV.”

Since the scare, South Nassau has implemented a hospital-wide policy that bans the use of insulin pens and now only permits single-patient-use vials to administer insulin treatments.

However, loved ones visiting patients at the hospital on Tuesday night were still frightened to hear this warning.

“It’s actually very scary,” said hospital visitor Andra Vetro, “because you come to the hospital when you’re sick, and you don’t hope to get even worse while you’re inside the hospital.”

The hospital said while the testing process is voluntary, it is recommended. The hospital will be offering the patients free and confidential blood testing services, and asked patients to schedule a blood test within 60 days of receiving the letter.